1. Field of the Invention
Aspects of the present invention relate to an organic electrolytic solution comprising a cycloolefin monomer and a lithium battery employing the same, and more particularly, to an organic electrolytic solution comprising a cycloolefin monomer that can be polymerized to form a polymer film that can prevent decomposition of an electrolyte and a lithium battery with improved cycle and lifetime characteristics by employing the organic electrolytic solution.
2. Description of the Related Art
As portable electronic devices, such as video cameras, cellular phones, notebook computers, and the like become more lightweight and are of increasingly higher performance, more research into batteries used as power supplies for such portable devices is being conducted. In particular, chargeable lithium secondary batteries have three times the energy density per unit weight than conventional lead storage batteries, nickel-cadmium batteries, nickel-hydrogen batteries, nickel-zinc batteries, and the like, and can be rapidly charged. Therefore, research and development of chargeable lithium secondary batteries is being actively conducted.
A lithium battery is generally driven at a high operating voltage, and thus a conventional aqueous electrolytic solution cannot be used. This is because lithium contained in an anode reacts vigorously with an aqueous solution. Thus, instead of an aqueous electrolytic solution, an organic electrolytic solution in which a lithium salt is dissolved in an organic solvent is used in the lithium battery. In this case, organic solvents having a high ionic conductivity and dielectric constant and a low viscosity may be used. Since it is difficult to obtain a single organic solvent satisfying all these requirements, a solvent including a mixture of an organic solvent having a high dielectric constant with an organic solvent having a low viscosity, or the like are generally used.
When a lithium secondary battery uses a carbonate-based polar non-aqueous solvent, a reaction of an anode with an electrolytic solution requires excess charges during initial charging. As a result of such an irreversible reaction, a passivation layer, such as a solid electrolyte interface (SEI) membrane, is formed on the surface of an anode. The SEI membrane allows the battery to be stably charged and discharged without further decomposition of the electrolytic solution. In addition, the SEI membrane acts as an ion tunnel through which only lithium ions pass and prevents co-intercalation of an organic solvent, which solvates lithium ions and moves with the lithium ions, into an anode, thereby preventing a breakdown of the anode structure.
However, as the lithium battery is repeatedly charged and discharged at a high voltage of 4 V or more, the SEI membrane gradually cracks due to expansion and contraction of an active material, which occurs during the charging and discharging, and becomes detached from the surface of the electrode. Thus, as shown in FIG. 1, an electrolyte directly contacts the active material, resulting in continuous decomposition of the electrolyte. In addition, once the crack of the SEI membrane occurs, the crack progresses due to the charging and discharging of the lithium battery, resulting in degradation of the active material. As a result, the SEI membrane formed of only a polar solvent and a lithium salt cannot retain the ideal properties described above. Accordingly, the internal resistance of the anode increases, and consequently, the capacity of the battery decreases. In addition, due to decomposition of the solvent, the amount of the electrolyte is reduced. Thus, the electrolyte in the battery becomes depleted, so that it is difficult to obtain sufficient ion transfer.
To address these and/or other problems, there is still a desire to develop a method of preventing direct contact between an anode active material and an electrolyte while not allowing degradation of conducting properties of lithium ions, thereby improving charge and discharge characteristics of a battery.